The hybridoma medium with l-glutamine, and 10% (v/v) FBC (Biochrom, AG) plus hypoxanthine–aminopterin–thymidine (HAT) or hypoxanthine–thymidine (HT) (Sigma), was used to select hybrids. Fusions to generate antibody-producing hybridomas GKT137831 were performed according to standard methods (Köhler & Milstein, 1975). The fusion mixture was then slowly diluted with 25 mL of RPMI 1640 solution. After centrifugation (400 g, 10 min), the cells were resuspended in 75 mL of hybridoma medium with HAT and dispensed in 200-μL aliquots in 6 × 96-well plates (Corning, New York). The hybridoma medium

with HAT was changed after 7 days to hybridoma medium with HT. After 10–14 days of growth in this medium, culture supernatants were tested using an ELISA test, with OPS from S. Dakar

(O281283) and S. Telaviv (O281282). The ELISA test (enzyme-linked immunosorbent assay) was carried out in 96-well plates (C96 Maxisorp, Nunc, Denmark). The plate wells were coated overnight with 10 μL per well antigens (S. Dakar OPS and S. Telaviv OPS) diluted in carbonate buffer (50 mM), pH 9.6, at 4 °C, and tested against serial dilutions of MAb. Antibody binding was detected with peroxidase-conjugated goat anti mouse immunoglobulins (Dako A/S, Denmark) and substrate OPD (Sigma Fast™ OPD) and measured photometrically at 492 nm. For ELISA inhibition, the MAbs in dilution 1 : 20 were preincubated with an inhibitor (LPS and OPS of S. Dakar and S. Telaviv, 20 μg PFT�� molecular weight per well) at 4 °C in 96-well plates overnight. Then, the antibodies were transferred to the plate containing the antigens mentioned, and the ELISA test was performed as earlier. Isotyping of MAbs was performed using the test ImmunoPure® Monoclonal Antibody Isotyping Kit I (HRP/ABTS; Pierce). For SDS-PAGE (Laemmli, 1970), an

LPS suspension (1.0 mg mL−1) mixed with a sample buffer (0.1 M Tris–HCl–20 mM EDTA, pH 6.8, containing 8% SDS, 20% glycerol and 0.001% bromophenol blue) was boiled for 20 min, and appropriate portions of LPS were applied to a gel. Electrophoresis was performed in a 15% acrylamide slab gel and 5% acrylamide stacking gel with PLEKHM2 a constant current of 30 mA per gel. LPS was detected in the gel by the silver-staining method (Hitchcock & Brown, 1983). The structures of the repeating units of S. Dakar OPS and S. Telaviv OPS are presented in Fig. 1. Salmonella Dakar OPS has a regular structure of pentasaccharide units (Fig. 1a), whereas the S. Telaviv O-polysaccharide has a much more complicated chemical structure (Fig. 1b), with 25% of the main chain β-d-Galp linked in position 3 to a digalactose [α-d-Galp-(13)-α-d-Galp-(1)] branching chain, while terminal Glcp substitutes 55% of the GalpNAc units in position 4. Separation of the water-soluble carbohydrate products on a Bio-Gel P-100 column yielded three fractions of S. Telaviv OPS with different molecular weights: HMW S.